Blowing agent additive containing azodicarbonamide and an aromatic sulfinic acid

ABSTRACT

Aromatic sulphinic acids and their salts are used as activators for lowering the decomposition temperature of azodicarbonamide, which have a higher activity than the conventional auxiliary blowing agents. Moreover, no premature liberation of gas takes place.

United ttes atet [191 R005 et al.

[ Sept. 2, 1975 BLOWING AGENT ADDITIVE CONTAINING AZODICARBONAIVHDE AND AN AROMATIC SULFINIC ACID [75] Inventors: Ernst Roos; Theo Kempermann,

both of Cologne; Manfred Abele, Porz-Wahn; Gunter Dammann, Cologne, all of Germany [73] Assignee: Bayer Aktiengesellschaft,

Leverkusen, Germany [22] Filed: Mar. 22, 1974 [21] Appl. No.: 453,933

Related US. Application Data [62] Division of Ser. No. 218,239, Jan. 17, 1972, Pat. No.

[58] Field of Search 252/350; 264/DIG. 5; 260/25 R, 513.7, 2.5 HA, 2.5 HB, 2.5 H, 260/25 AB, 724

[56] References Cited OTHER PUBLICATIONS Blowing Agents; Henry R. Lasman; Encyclopedia of Polymer Science and Technology p. 548.

Primary ExaminerBenjamin R. Padgett Assistant ExaminerDavid Leland Attorney, Agent, or FirmConnolly and Hutz [5 7] ABSTRACT Aromatic sulphinic acids and their salts are used as activators for lowering the decomposition temperature of azodicarbonamide, which have a higher activity than the conventional auxiliary blowing agents. Moreover, no premature liberation of gas takes place.

6 Claims, 1 Drawing Figure 1b 2b 3b 50 6b 7'0 A BLOWING AGENT ADDITIVE CONTAINING AZODICARBONAMIDE AND AN AROMATIC SULFINIC ACID CROSSREFERENCE TO RELATED APPLICATION This application is a division of application Ser. No. 218,239 filed Jan. 17, 1972, now U.S. Pat. No. 3,803,060.

This invention relates to aromatic sulphinic acids and their salts as activators for lowering the decomposition temperature of azodicarbonamide which is used as chemical blowing agent for the production of cellular or porous articles based on natural or synthetic rubber and plastics. (See Angewandte Chemie 64 [1952] pages 65-76).

The choice of a suitable chemical blowing agent for the production of cellular or porous articles based on rubber or plastics is determined primarily by the temperature at which the blowing agent decomposes to liberate gas. Azodicarbonamide has a decomposition temperature in the range of 200C to 210C. When it is present in mixtures, gas starts to be evolved at about 160C (loc. cit., page 70, righthand column). In many cases, however, it is desired for decomposition of azodicarbonamide to take place at lower temperatures than this. Decomposition at a lower temperature would reduce the thermal stresses to which mixtures foamed with azodicarbonamide are subjected and would also enable higher decomposition rates and shorter operating cycles to be achieved.

It is already known that the decomposition temperature of azodicarbonamide is reduced by the addition of one or more so-called auxiliary blowing agents which have a lower decomposition temperature than azodicarbonamide (see German Offenlegungsschrift No. 1,5 69,535)

The use of these auxiliary blowing agents, however, frequently results in premature decomposition of the blowing agent in the course of production and processing of the mixtures containing them because the auxiliary blowing agents used as activators for azodicarbonamide, for example benzene sulphohydrazide, decompose at relatively low temperatures, e.g. at 80C (see loc.cit. page 71, lefthand column, last paragraph). Consequently, unwanted decomposition of the auxiliary blowing agent may occur during storage of mixtures which contain such combinations of blowing agents. This is manifested e.g. in the case of rubber mixtures by premature expansion and in the case of plastics, e.g. PVC pastes, by gassing.

We now have found that aromatic sulphinic acids and their salts represented by the following general formula wherein M represents hydrogen, a metal cation or a group which contains ammonium nitrogen;

n represents the valency of M; and

R to R represents, independently of each other, hy-

drogen, straight chain or branched chain alkyl groups with from I to 4 carbon atoms, or halogen atoms may be used in the production of cellular or porous natural and synthetic rubber or plastic, i.e. synthetic resin articles carried out in the presence of azodicarbonamide as a blowing agent.

The sulphinic acids and sulphinates used according to the invention surprisingly function as activators in lowering the decomposition temperature of azodicarbonamide used as blowing agent and in this respect they have a higher activity than the conventional auxiliary blowing agents such as benzene sulphohydrazide. Moreover, they do not give rise to premature liberation of gas since they are not themselves blowing agents.

The following are mentioned as examples of radicals R to R Straight chain or branched chain alkyl groups having from 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec.butyl, tert.-butyl or isobutyl; the halogen atoms may be chlorine, fluorine wherein R R and R represent, independently of each other, hydrogen or an aliphatic radical, the radicals R and R may together with the ammonium nitrogen form part of a 5, 6 or 7-membered ring system which in the case of a 6-membered ring may in addition contain hetero atom such as oxygen, a nitrogen atom optionally substituted by a C to C alkyl radical or a sulphur atom.

The aliphatic radicals R to R may be straight chain or branched chain alkyl radicals having 1 to 4 carbon atoms optionally substituted by phenyl or they may be cycloalkyl radicals with from 5 to 7 carbon atoms. The following are mentioned as examples of alkyl and cycloalkyl radicals: Methyl, ethyl, n-propyl, isopropyl, nbutyl, sec.-butyl, isobutyl, tert.-butyl, benzyl, phenylethyl, phenyl-n-propyl, cyclopentyl, cyclohexyl and methylcyclohexyl.

The following are mentioned as specific examples of compounds which may be used according to the invention:

Benzene sulphinic acid; lithium benzene sulphinate; sodium benzene sulphinate; potassium benzene sulphinate;

magnesium-di(benzene sulphinate); calcium di-(benzene sulphinate); zinc-di-(benzene sulphinate); barium di(benzene sulphinate); cadmium di(benzene sulphinate); lead di-(benzene sulphinate); ammonium benzene sulphinate; trimethylammonium benzene sulphinate; tertiary butyl ammonium benzene sulphinate; cyclohexyl ammonium benzene sulphinate; benzyl ammonium benzene sulphinate; p-toluene sulphinic acid; lithium p-toluene sulphinate; sodium ptoluene sulphinate; potassium p-toluene sulphinate; magnesium bis-(p-toluene sulphinate); calcium bis-(p-toluene sulphinate); barium bis(p-toluene sulphinate); zinc bis-(p-toluene sulphinate); cadmium bis(p-toluene sulphinate); lead bis-(p-toluene sulphinate);

ammonium p-toluene sulphinate; diethylammonium p-toluene sulphinate; di-sec.-butylammonium p-toluene sulphinate; cyclohexyl-methylammonium-p-toluene sulphinate; morpholinium-p-toluene sulphinate; thiomorpholinium-p-toluene sulphinate; piperazinium-p-toluenesulphinate; p-chlorobenzene sulphinic acid; lithium-p-chlorobenzene sulphinate; sodium-p-chlorobenzene sulphinate; potassium p-chlorobenzene sulphinate; magnesium bis-(p-chlorobenzene sulphinate); calcium bis-(p-chlorobenzene sulphinate); barium bis-(p-chlorobenzene sulphinate); zinc bis-(p-chlorobenzene sulphinate); cadmium bis-(p-chlorobenzene sulphinate); lead bis-(p-chlorobenzene sulphinate); ammonium p-chlorobenzene sulphinate; triethylammonium p-chlorobenzene sulphinate; dicyclohexylammonium p-chlorobenzene sulphinate; pyrrolidinium-p-chlorobenzene sulphinate; piperidinium-p-chlorobenzene sulphinate; 2,4dimethylbenzene sulphinic acid; lithium 2,4-dimethylbenzene sulphinate; sodium 2,4-dimethylbenzene sulphinate; potassium 2,4-dimethylbenzene sulphinate; magnesium-bis-(2,4-dimethylbenzene sulphinate); calcium-bis-( 2,4-dimethylbenzene sulphinate); barium bis-(2,4-dimethylbenzene sulphinate); zinc-bis-( 2,4-dimethylbenzene sulphinate); cadmium-bis-(2,4--dimethylbenzene sulphinate); lead-bis(2,4-dimethylbenzene sulphinate); ammonium 2,4-dimethylbenzene sulphinate; 2,5-dimethylbenzenc sulphinic acid; sodium 2,5-dimethylbenzene sulphinate; zinc bis-(2,5-dimethylbenzene sulphinate); 3,4-dimethy1benzene sulphinic acid; sodium 3,4-dimethylbenzene sulphinate; zinc bis-(3,4-dimethylbenzene sulphinate); 2-chloro-4-methyl-benzene sulphinic acid; sodium 2-chloro-4-methyl-benzene sulphinate; zinc bis-( 2-chloro-4-methylbenzene sulphinate); Z-methyl-4-chloro-benzene sulphinic acid, sodium 2-methyl-4-chloro-benzene sulphinate; zinc bis-(2methyl-4-chloro-benzene sulphinate); p-fluorobenzene sulphinic acid;

sodium p-fluorobenzene sulphinate;

zinc bis-(p-fluorobenzene sulphinate);

p-bromobenzene sulphinic acid;

sodium p-bromobenzene sulphinate;

zinc bis-(p-bromobenzene sulphinate);

p-tertiary butyl-benzene sulphinic acid;

sodium p-tertiary-butyl-benzene sulphinate;

Zinc bis-(2,3,4,5,o-pentamethyl-benzene sulphinate);

and

zinc bis-(2,3,4,5,6-pentachloro-benzene sulphinate).

Suitable rubbers and plastics for the production of cellular or porous articles using azodicarbonamide and activators based on sulphinic acids or sulphinates are e.g. natural rubber or synthetic, rubber-like polymers obtained e.g. from conjugated diolefines such as butadiene, chlorobutadiene, dimethylbutadiene, isoprene and its homologues; or copolymers of such conjugated diolefins with polymerisable vinyl compounds such as styrene, oz-methyl styrene, acrylonitrile, methacrylonitrile, acrylates or methacrylates; polymers such as polyethylene, polypropylene, polyvinyl chloride, polyvinyl acetate, polyvinyl chloride acetate, polystyrene, polyacrylonitrile, acrylonitrile-butadiene-styrene copolymers, ethylene-vinyl acetate copolymers, ethylenepropylene terpolymers, for example with dienes as tercomponent, ethylene-propylene copolymers, vinyl chloride-ethylene copolymers, vinyl chloridepropylene copolymers, polyurethanes and mixtures of the above mentioned polymers.

The activators to be used according to the invention may be mixed with the foaming mixtures in the usual manner, for example on mixing rollers at temperatures from l20l50C by mixing for 530 minutes, in internal mixers at room temperature by mixing for 5-30 minutes or in mixing vessels equipped with stirrers at room temperature by mixing for 5-120 minutes. The activators may be added at the same time as the other constituents of the mixture but are preferably added at the start, that is from when azodicarbonamide is first used as blowing agent. The quantity of activators used according to the invention should be in the range of from about 0.5 to 30 percent by weight, preferably 2 to 10% by weight, based on the blowing agent, in the case of mixtures based on natural or synthetic rubber. In cases where synthetic resins are used, e.g. polyethylene, polypropylene, polyvinyl chloride or polystyrene, the quantity of activators used according to the invention should by in the range of from about 0.1 to 5 parts by weight, preferably 0.5 to 3.0 parts by weight, based on 1 part by weight of the blowing agent.

After addition to natural and/or synthetic rubber the mixtures thus obtained are heated at the usual vulcani- Zation temperatures from 130 to 300C.

After addition to plastics the expansion according to the invention takes place after heating at temperatures from 160 to 220C. If necessary the crude material can be expanded again at temperatures from to C.

When using a pressureless process films and pastes pass through a gelatinizing channel heated to 120250C for a period of 0.5l0 minutes.

The mixtures which are to be treated may also contain conventional auxiliary agents, e.g. active or inactive fillers such as carbon black or chalk, antioxidants, antiozonants, stabilizers such as salts of lead, cadmium, calcium, zinc, tin or barium, waxes, dyes pigments, zinc oxide, fatty acids such as stearic acid, mineral oils, plasticizers such as dioctyl phthalate, butyl no yl phthalate, butyl benzyl phthalate, dibutyl phthalate, dibutyl adipate or tricresyl phosphate, lubricants, peroxides, vulcanizing agents such as sulphur and accelerators. The following are examples of suitable accelerators: Thiazoles, guanidines, dithiocarbamates, thiurams and 2- mercaptoimidazoline.

The method of preparing the aromatic sulphinic acids and their salts (I) is already known.

The alkali metal salts may be prepared e.g. by reacting aromatic sulphonic acid chlorides with an alkali metal sulphite in aqueous alkaline solution, for example in accordance with the following reaction equation:

S0 Na Na SO NaCl H O Aromatic sulphinates which are only sparingly soluble in water can easily be obtained by double decomposition of the above mentioned alkali metal sulphinates in aqueous solution with those metal salts which form such sparingly soluble aromatic sulphinates, e.g. according to the following equation:

2 CH;, Q so Na ZnCb-(CH s0 Zn 2 NaCl.

The alkali metal salts may also advantageously be used for the preparation of free aromatic sulphinic acid, e.g. according to the following equation:

Ammonium sulphinates are obtained by reacting the free sulphinic acids with ammonia in accordance with Substituted ammonium sulphinates are obtained by reacting the free sulphinic acids with amines such as the deprotonised compounds of formula (II). The following reaction equation illustrates by way of example the reaction of p-toluenesulphinic acid with morpholine:

The following Examples serve to illustrate the invention. The figures entered in the Tables represent parts by weight unless otherwise indicated.

EXAMPLE 1 The graphs in FIG. 1 represent the rate of liberation of gas from the azodicarbonamide alone and with the aid of various activators. The rate of liberation of gas was determined on the principle of molecular weight determination by the method of Victor Meyer.

Curve A of the drawing represents the rate of decomposition of l g of pure azodicarbonamide suspended in 1 g of tricresyl phosphate at 192C.

Curve B of the drawing represents the rate of decomposition of 1 g of a mixture of 0.9 g of azodicarbon amide and 0.1 g of benzene sulphonhydrazide suspended in l g of tricresyl phosphate at 192C.

Curve C of the drawing represents the rate of decomposition of l g of a mixture of 0.9 g of azodicarbonamide and 0.1 g of zinc dibenzene sulphinate suspended in l g of tricresyl phosphate at 192C.

The curve clearly shows that zinc di-benzene sulphinate accelerates the decomposition of azodicarbonamide for a greater extend than benzene sulphohydrazide.

EXAMPLE 2 the following equation: The following mixtures were prepared (see Table l Table l Mixture No. 1 2 3 4 5 6 7 8 9 10 1 1 Ethylenmpropylene-diene terpolymer 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Zine oxide 5.0 5.0 5.0 50 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Steuric acid 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 fine carbon black 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 powdered chalk 75.0 75.0 75.0 75.0 75.0 75.0 75.0 75.0 75.0 75.0 75.0 nllphlhCniC mineral oil 75.0 75.0 75.0 75.0 75.0 75.0 75.0 75.0 75.0 75.0 75.0 Z-mcrcuptnbcnzothiuzole 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 tctrumethylthiuramic monosulphidc 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 N N-diphenylthioureu 1.0 1.0 1,0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 sulphur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 azodicarbonamide 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 benzene sulphohydrazide) (for comparison) 0. 5 zinc di-(henzene sulphinatc) 0.15 sodium benzene sulphinate 0 15 zinc bis(p-chlorobenzene sulphinate) 015 lead di henzcne sulphinate) 0.15

cadmium -i toluene sulphinate) Table l -Continued Mixture No. 1 2 3 4 5 6 7 8 9 10 1 1 cadmium iii-(benzene sulphinate) 0.15 sodium toluene sulphinatc 0.15 Magnesium di-(benzenc sulphinute) 0.15 sodium pchlorobenzcne sulphinate 0.15

The mixtures were prepared on mixing rollers and ex- The components of the mixture were homogenized truded to form profiles of constant cross-section. These 10 f r 1 minu es n miXing rollers hea d to 1 5 an profiles were then placed in a suitable vulcanizing then removed in the form of a foil. The resulting foil mould. The unvulcanized profiles were cut into equal was then gelatinized in a gelatinizing channel heated lengths before being introduced into the moulds and with circulating air at 190C to effect complete gelationly partly filled the moulds so that complete filling of nization and foamed at the same time. The time of stay the moulds during and after vulcanization was possible in the curing oven was 2 minutes.

only after complete liberation of gas from azodicarbon- The results obtained with formulations 12 to 23 are amide. Vulcanization was carried out in a press at summarized in the Table below.

Mixture No. 12 13 14 15 I6 17 18 19 20 21 22 23 Density (g/cm) 0.44 0.22 0.25 0.74 0.60 0.62 1.04 0.67 0.65 1.03 0.37 0.55

160C for 20 minutes. It is clear that the mixtures containing azodicarbon- The densities (g/cm") of the vulcanized and ex- 25 amide as blowing agent and zinc di-(benzene sulphipand d pr files are h wn elo nate) or zinc di-(4-chloro-benzene sulphinates) as acti- Mixture No. 1 2 3 4 5 6 7 8 9 10 1 1 Density (g/Cm) 0.83 0.56 0.54 0.55 0.57 0.59 0.54 0.57 0.57 0.56 0.54

The figures in this table show that insufficient gas is vator result in products with a lower specific weight evolved from azodicarbonamide at 160C without an than the corresponding comparative formulations.

Table 2 Mixture No. 12 13 14 15 16 17 18 19 20 21 22 23 PVC paste for comparison (K value 55 55 55 approx. 70} Suspension PVC (K-value approx.70) 50 50 50 Ethylenewinyl acetate-vinyl chloride tcrpolymer 100 100 100 100 100 100 Alkylsulphonic acid ester of phenol 5 5 Polyurethane 50 50 Diisononylphthulute 20 20 20 Azodicarbonamidc Ba/Cd stabilizer (fl.)

Dibutyl tin mercaptide 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 10 Zinc di-(henzencsulphinutc) 1.5 1.5 1.5 1.5 Zinc di-(4-chlorobenzenc sulphinatc) 1.5 1.5 1.5 1.5 Chalk 5.0 5.0 5.0 5.0 5.0 5.0 Ester wax. partly saponificd 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 12 hydroxystcuric acid 0.2 0.2 0.2

activator present and consequently azodicarbonamide EXAMPLE 4 does not sufiiciently expand the mixture. In that case, a profile with relatively high density is obtained (mix- D ture No. 1.) All the other mixtures (Nos. 2 to l l which Mrxrures 24 to 37 represented Table 3 were contains activators in addition to azodicarbonamide Preparedcompletely filled the moulds. This is manifested by the The Components of the formulatron were homoge' low densities. The sur ri ing fi din i thi experiment nized on a three roll mill. The resulting paste was mtrois that the sulphinates used show the same activator efduced into a g -t g mould Where t s ated und r fect in a quantity of 5 percent (based on azodicarbonpr at C C p ly) r 2 m namide) as benzene sulphohydrazide in a quantity of 15 utes and then cooled under pressure. The resulting percent. product was then removed from the mould and blown up in a hot air atmosphere at 100C for 30 minutes.

EXAMPLE 3 65 The resulting densities of the end products obtained Mixtures Nos. 12 to 23 represented in Table 2 were from formulations 24 to 37 are entered at the end of prepared. Table 3.

The results show that mixtures which contain zinc di- (benzenesulphinate) or Zinc di-(4-chlorobenzene sulphinate) as activator give rise to products with a lower specific gravity than the corresponding formulations used for comparison both in the case where the blowing 5 agent used is azodicarbonamide and in the case where a mixture of azodicarbonamide and benzene sulphohydrazide in the ratio of 85 15.

The results obtained for formulations 38 to 51 are summarised in Tables 5 and 6.

It is clear from the results that when mixtures containing azodicarbonamide are applied in equal amounts (approximately 850 g/m those which also contain zinc di-(benzene sulphinate) or zinc di-(4- chlorobenzene sulphinate) result in products with a lower specific gravity than the products which are ob- Table 3 Mixture No. 24 25 26 27 28 29 30 31 32 33 34 35 36 37 Vinyl chloride-vinyl acetate copolymer suit- 50 50 able for preparing a paste PVC paste (N-value approx. 50 S0 50 50 50 50 50 50 50 5O 5O Di2-ethy1-hexyl phthalate 50 50 50 50 50 50 50 50 50 50 50 50 50 50 dibutyl tin mercaptide 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 zinc di-(benzenesulphinate) 1.5 1.5 0.5 1.5 1.5 zinc di-(4-ch1orobenzene sulphinate) 1.5 1.5 0.5 1.5 1.5 dibasic lead phthalate 1.5 1.5 sodium bicarbonate 1.0 1.0 1.0 1.0 1.0 1.0 azodicarbonamide 4.75 4.75 4.75 4.5 4.5 3.0 3.0 3.0 azodicarbonamide/benzene sulphohydrazide :15 5 5 5 3.0 3.0 3.0

Density(g/cm) at C 0.41 0.12 0.11 1.18 0.21 0.19 0.25 0.25 DensilYQ/Cm) at C 0.36 0.19 0.18 0.24 0.23 020 0.16 0.16 0.21 0.18 0.18

EXAMPLE 5 tained from the corresponding comparative mixtures.

nized in a gelatinizing channel heated with circulating 40 air and foamed up.

The residence times of the mixtures which were to be foamed and the temperature in the gelatinizing channel were varied This effect is all the more obvious the shorter the time of stay in the gelatinizing channel.

In addition, it is observed that such mixtures give rise to products with a substantially higher proportion of open pores than those which contain e.g. a dibasic lead phthalate as activator.

The same applies to mixtures which contain as blowing agent a mixture of azodicarbonamide and benzene sulphohydrazide in the proportion of 85:15 instead of azodicarbonamide alone.

Similar results are obtained when the gelatinizing temperature is varied instead of the time of stay.

Table 4 Mixture No. 39 4O 41 42 Table 5 Density (g/cm) 12 The results show that the plates produced from azodicarbonamide without activator have undergone only slight expansion whereas the activators used effect dis- Mixture No. at time of stay in minutes in gelatinizing Channel temperature 190C tinctly more rapid liberation of gas, which is expressed 3.43 2.66 l 71 1.33 l 5 by the lower densities of the product. It should be noted 38 050 064 0.88 094 L08 that the activators used according to the invention 39 0.33 0.34 0.35 0.42 0.83 (mixtures 54 and 55) produce the same effect at lower 40 0.34 0.35 0.38 0.39 0.51 41 034 Q35 O37 039 05] doses as benzene sulphohydrazlde (mixture 53). 42 0.64 0.73 0.89 0.92 1.09 43 0.33 0434 0.42 0.54 0.92 44 0.40 0.4| 0.43 0.48 0.62 EXAMPLE 7 45 0.39 0.39 0.39 0.45 065 The following mixture was prepared (Table 8) Table 6 Table 8 Mixture N04 Density (g/cm) at time of stay 3043 minutes in gelatinizing channel in dependence upon the temperature Mi N 56 140C 150C 160C Polychloroprene rubber 100,0 Magnesium oxide 46 20 Diphenylamine derivative 1,5 47 Medium thermal black 200 48 Alkylsulphonic acid ester of phenol 30,0 2: 8'2 Powdered chalk 45,0 Stearic acid 10 51 0493 0.79 058 Zinc oxide N.Ndiphenylthiourea 1,0 25 2-Mercaptoimidazoline 1,0 EXAMPLE 6 Azodicarbonamide 2,7 Zinc-di-(benzene sulphinate) 0,3 The following mixtures were prepared (see Table 7) Table 7 Mixture NO 52 53 54 55 Styrene-butadiene copolymer (styrene content approx. 23.5%) 70.0 70.0 70.0 70.0 Styrene-butadiene copolymer (styrene content approx. 30.0 30.0 30.0 30.0 Coumarone resin 50 5.0 5.0 5.0 Precipitated silicic acid containing a small proportion 45.0 45.0 45.0 45.0 of calcium silicate Aromatic mineral oil 2.5 2.5 2.5 2.5 Zinc oxide 5.0 5.0 5.0 5.0 Stearic acid 3.0 3.0 3.0 3.0 Ethylene glycol 1.1 1.1 1.] 1.1 Diphenylamine derivative 1.0 1.0 1.0 1.0 Sulphur 2.5 2.5 2.5 245 2-Mercaptobenzothiazole 1.5 1.5 1.5 1.5 Azodicarbonamide 3.5 3.5 3.5

Azodicarbonamidc/benzenesulpho- 35 hydrazide 15 Zinc di-(benzene sulphinate) 0.175 Zinc bis-(p-chlorobenzene sulphinate) I 0.175

The mixtures were prepared on mixing rollers and The mixture was prepared on mixing rollers and exrolled out into plates about 10 mm in thickness. 420 g truded to form a profil. This profil was then placed in of each mixture were then introduced into a mould 50 a suitable vulcanizing mould and only partly filled it. measuring 200 mm X 200 mm X 8 mm (corresponding vulcanization was carried out in a steam-heated press to filling the mould by 103 volumes percent) and then at 160C for 20 minutes. pre-cured for 12 minutes at 150C at a pressure of 80 The vulcanized and expanded profile has a density of kg wt/cm in a steam heated press. The plates were re- 0.52 g/cm moved from the mould at the end of this time and were 55 found to have undergone substantial expansion. These EXAMPLE 8 expanded plates were then placed in a hot air chamber The following mixtures were prepared (Table 9) (C) for 30 minutes to complete curing.

After cooling, the plates were split in a splitting ma- Table 9 chine and the samples obtained were tested to deter- 60 mine their density and hardness. The following results M'Xtum 57 58 were Obtained: Ethylene vinyl acetate copolymcr 100,0 100,0 Powdered Chalk 20,0 20,0 Mixture No. 52 53 54 55 y 20,0 201) 4 Stearic acid 1,0 1.0 DQ115113 (g/ (X69 0445 65 1.3-Bis-(tertiary butyl peroxi)-iso- 1.0 1.0 HilfdflCSS (S w A) propylhcnzcne (40 /1) Outer skin 67 54 51 52 Azodicarbonzlmidc 5.0 4.5 Split surface 60 46 42 44 Zinc-di-( benzene sulphinate) 0.

The mixtures were prepared on mixing rollers. The mixing temperature was about 8090C. The peroxide was added finally at about 7080C. The mixtures were then rolled out into plates about 7 mm in thickness and 330 g of each introduced into a mould measuring 200 mm X 20 mm X 6 mm (corresponding to filling the mould by 100 volumes percent).

In this way two plates per mixture were placed and then heated for 8 minutes,'respective1y 12 minutes at 160C at a pressure of 80 kg wt/cm on the surface of the mouldings.

At the end of the cited time the plates were removed from the mould and were found to have undergone substantial expansion. After cooling, the plates were split in a splitting machine and the samples obtained were tested to determine their density and hardness. The following results were obtained:

Mixture No. 57 58 Heating time for 8 min. at 160C Density (g/cm") practically no 0.21 Hardness (Shore A) expansion 33 Heating time for 12 min. at 160C Density (glcm about 0,9 0.19 Hardness (Shore A) about 80 30 The results show that the plates produced from azodicarbonamide without activator have undergone only slight, respectively no expansion whereas the activator zinc-di-(benzene sulphinate) used effect distinctly more rapid liberation of gas which is expressed by the lower densities of the product.

EXAMPLE 9 To produce extruded articles made of polyethylene the commercially available granulates are mixed in suitable mixing devices such as internal mixers with 0.3-0.4 butyl stearate as an adhesive agent. Mixing time -30 minutes, preferably 10 minutes. Thereafter the activator and the azodicarbonamide are added. Any possible stickiness of the granulate can be prevented by 45 hour storage at 50 to 70C.

The processing conditions have been correctly choosen if the extruded or injection-moulded materials leave the extrusion orifize or the nozzle as a bubblefree melt and if the foaming process starts 1-5 cm away from the orifice or if the foaming takes place upon injection moulding 1-5 cm after injecting into the free space.

Temperature program for the extruder:

Feed zone: 130 150C Compression zone: 150 170C Metering zone: 180 190C Injection mould: 130 155 180C starting from the feeding hopper Nozzle: maximum 220C Density of the parts obtained: 0.4-0.5 g/cm What we claim is:

wherein M is hydrogen, a metal cation or a group containing an ammonium nitrogen,

n is the valency of M and R to R are, independently of each other, hydrogen,

alkyl groups having 1 to 4 carbon atoms or halogen.

2. The activated blowing agent of claim 1 wherein said compound of said formula is zine di-(benzene sulphinate).

3. An activated blowing agent useful for the production of cellular or porous articles of synthetic resins, said activated blowing agent comprising azodicarbonamide and, for each part by weight of azodicarbonamide, 0.1 to 5 parts by Weight of a compound of the formula wherein M is hydrogen, a metal cation or a group containing an ammonium nitrogen,

n is the valency of M and R to R are, independently of each other, hydrogen,

alkyl groups having 1 t0 4 carbon atoms or ha1ogen.

4. The activated blowing agent of claim 3 wherein said compound of said formula is zinc di-(benzene sulphinate).

5. The activated blowing agent of claim 3 wherein said compound of said formula is present in an amount of from 0.5 to 3.0 parts by weight for each part by weight of azodicarbonamide.

6. The activated blowing agent of claim 5 wherein said compound of said formula is zinc di-(benzene sulphinate). 

1. AN ACTIVATED BLOWING AGENT USEFUL FOR THE PRODUCTION OF CELLULAR OR POROUS ARTICLES OF AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF NATURAL RUBBER AND SYNTHETIC RUBBER, SAID ACTIVATED BLOWING AGENT COMPRISING AZODICARBONAMIDE AND FROM 0.5 TO 30 PERCENT BY WEIGHT, BASED ON THE WEIGHT OF SAID AZODICARBONAMIDE OF A COMPOUND OF THE FORMULA
 2. The activated blowing agent of claim 1 wherein said compound of said formula is zinc di-(benzene sulphinate).
 3. An activated blowing agent useful for the production of cellular or porous articles of synthetic resins, said activated blowing agent comprising azodicarbonamide and, for each part by weight of azodicarbonamide, 0.1 to 5 parts by weight of a compound of the formula
 4. The activated blowing agent of claim 3 wherein said compound of said formula is zinc di-(benzene sulphinate).
 5. The activated blowing agent of claim 3 wherein said compound of said formula is present in an amount of from 0.5 to 3.0 parts by weight for each part by weight of azodicarbonamide.
 6. The activated blowing agent of claim 5 wherein said compound of said formula is zinc di-(benzene sulphinate). 